1. Field of the Invention
This invention relates to internal combustion engines, in general, and particularly to fuel injected diesel cycle engines. More specifically, the present invention relates to the construction of the cylinder block and cylinder liner to accommodate cooling of the liner.
2. Description of the Related Art
It is conventional practice to provide the cylinder block of an internal combustion engine with numerous cast-in-place, interconnected coolant passages within the area of the cylinder bore. Coolant fluid is circulated through these passages to maintain the engine block temperature at a predetermined acceptably low range, thereby precluding excessive heat distortion of the piston cylinder, and related undesirable interference between the piston assembly and the piston cylinder.
However, in conventional diesel engines having replaceable cylinder liners of the flange-type, coolant is generally not in contact with the upper margin or top portion of the liner, but rather is restricted to contact below the support flange in the cylinder block. This support flange is normally, and necessarily, of substantial thickness. The upper margin of the cylinder liner spans the area of the combustion chamber defined by the piston and the cylinder. Thus, the upper margin is the most highly heated portion of the cylinder liner and is not directly cooled.
Furthermore, uniform cooling all around the liner is difficult to achieve near the top, or upper margin, of the liner because the location of coolant transfer holes in the cylinder head is often restricted by other, overriding design considerations. The number of transfer holes is usually limited, and in many engine designs, the transfer holes are not uniformly spaced.
All of the foregoing has been conventional practice in internal combustion engines, and particularly with diesel cycle engines, for many years. However, in recent years there has been a great demand for increasing the horsepower output of the engine package. At the same time, there also exists demands to redesign certain engine components in an effort to improve emissions by lowering hydrocarbon content. Both of these demands result in hotter running engines, which in turn create greater demands on the cooling system.
As noted above, the most critical area of the cylinder liner spans the upper margin, and includes the top piston ring reversal point. The top piston ring reversal point is the top dead center position of the piston and is a point at which the piston is at dead stop or zero velocity. In commercial diesel engine operations, it is believed that the temperature at this piston reversal point must be maintained so as not to exceed 400xc2x0 F. (200xc2x0 C.). However, in meeting the demands for more power and fewer hydrocarbon emissions, the fuel injection pressure in a diesel cycle engine has been increased on the order of over 40% (from 20,000 psi to a range including 28,000-32,000 psi) and the engine timing has been retarded.
Collectively, these operating parameters make it difficult to maintain an acceptable piston cylinder liner temperature at its upper margin and corresponding to the top piston ring reversal point with the conventional cooling techniques described above. More specifically, and where no means for cooling the upper margin of the cylinder liner has been provided in the related art, a certain zone in the main cooling chamber approximately 90 degrees spaced from a given outlet has a tendency to be an area of stagnation with little or no coolant flow. Consequently, this zone was susceptible to producing hot spots on the liner. When cylinder liner temperatures exceed acceptable levels, coolant fluid can boil which increases its thermal loading and can lead to distortions and even scuffing of the cylinder liner. FIG. 6 graphically illustrates this point. Here, the temperature of the coolant and the cylinder liner (TLC) are presented as a function of coolant mass flow rate. The ability of the coolant to function decreases as it exceeds its boiling limit which, in turn, causes the temperature of the cylinder liner to increase, thereby increasing the risk of cylinder liner scuffing. Thus, in general, as operating temperatures in the combustion chamber have increased, so have the risk of cylinder liner scuffing failures due to inadequate cooling.
Attempts have been made in the past to address this issue. For example, U.S. Pat. No. 5,596,954 issued on Jan. 28, 1997; U.S. Pat. No. 5,505,167 issued on Apr. 9, 1996; and U.S. Pat. No. 5,299,538 which issued on Apr. 5, 1994 each disclose internal combustion engines having cylinder liners which are designed to improve coolant flow about the upper margins of the liners. Each of these patents is assigned to the assignee of the present invention and their disclosures are incorporated herein by reference. While the cylinder liners and methods of cooling the liners disclosed in these patents represent significant improvements over the liners and methods known in the related art, as the operating temperatures and pressures of the internal combustion engines continue to increase, there has remained a need to find additional ways to reduce the thermal loading on coolant fluid thereby maintaining the temperature of the cylinder liner within acceptable ranges.
Recently, it has also been determined that variation in liner temperature from cylinder to cylinder in a given engine block is a function of coolant mass flow distribution in the cylinder head. More specifically, FIG. 7 illustrates the effect of exhaust gas temperature on coolant temperature for cylinder liners known in the related art. The position or height of the curve relative to the y-axis depends on engine load and injection timing (i.e. gas temperature), and the coolant mass flow rate, which, in turn depends upon engine pump speed. Together, these parameters determine the operating point on the curve. At a given engine speed and constant mass flow represented by the vertical line at 0.015 kg/s in FIG. 7, the coolant temperature will be determined by where the mass flow line intersects the operating curve. If the lower curve represents peak torque operation at ratings known in the related art (reference gas temperature), and the upper curve represents projected peak torque operation at future high torque ratings (high gas temperature), then the coolant temperature will increase from below boiling to above boiling due to the torque rating increase. Thus, it is projected that in order to maintain coolant temperatures below the boiling point using known cylinder liner coolant designs, the mass flow of the coolant must be increased until the operating point on the top curve moves below the coolant boiling limit. In turn, this requires increased pump capacity or an alternative cylinder liner coolant design adapted to handle the higher temperatures induced at the higher engine operating parameters. While a high flow pump is one method of increasing the coolant mass flow rate, this approach suffers from the disadvantage that it increases parasitic losses for the engine.
Thus, there remains a need in the art for a cylinder liner which facilitates adequate cooling via increased coolant mass flow which is sufficient to accommodate the ever-increasing operating temperatures in internal combustion engines and, particularly, those using the diesel engine cycle.
The present invention overcomes the deficiencies in the related art in an internal combustion engine including a cylinder block having at least one cylinder bore. The internal combustion engine includes a cylinder liner which is concentrically disposed within the cylinder bore and secured to the cylinder block. The cylinder liner includes a main body portion and an upper margin thereof. A main cooling chamber surrounds a substantial portion of the main body portion of the cylinder liner and has an inlet port and at least one outlet port for circulating a coolant fluid about the main body portion of the cylinder liner. Furthermore, the cylinder liner includes a secondary cooling chamber located about the circumference of the upper margin of the cylinder liner. The secondary cooling chamber includes four inlet ports in fluid communication with the main cooling chamber and which are disposed spaced from one another at equidistant points about the circumference of the cylinder liner. In addition, the secondary cooling chamber includes four outlet ports providing fluid communication with the outlet port of the main cooling chamber. The four outlet ports of the secondary cooling chamber are disposed spaced from one another at equidistant points about the circumference of the cylinder liner and between adjacent ones of the inlet ports. Furthermore, the secondary cooling chamber is defined by eight discrete segments extending between the four inlet ports and the four outlet ports such that fluid coolant is circulated from each of the four inlet ports in opposite directions through adjacent segments of the secondary cooling chambers toward a pair of the four outlets.
One advantage of the internal combustion engine having a cylinder liner cooling chamber of the present invention is that the mass flow of coolant within the cooling chamber is increased. Another advantage of the internal combustion engine having the cylinder liner cooling chamber of the present invention is that the resident time of the fluid within the eight discrete segments of the secondary cooling chamber is reduced relative to that of the related art. This results in a lower coolant temperature and, concomitantly, a lower liner temperature when compared with other designs known in the related art employing the same mass flow rate. Thus, the cylinder liner of the present invention is significantly less sensitive to variations in the coolant mass flow rate and the coolant fluid can absorb more thermal loading before boiling. The internal combustion engine employing the cylinder liner having cooling chambers of the present invention achieves these advantages while at the same time enjoying a relatively low pressure drop between the inlet to the secondary cooling chamber and the outlet to the main cooling chamber.
The engine block having the secondary cooling chamber of the present invention provides a uniform, high velocity stream of coolant fluid all around the upper margin of the cylinder liner which effectively cools the area of the liner adjacent to the top piston ring reversal point. This, in turn, tends to better preserve the critical lubricating oil film on the liner inside surface. A resulting uniform cooling also minimizes the liner bore distortion, leading to longer service life. Thus, the engine block having the secondary cooling chamber of the present invention provides optimum heat removal characteristics at both the gas or combustion side of the cylinder wall, which reduces oil deterioration, excessive wear and the like, as well as at the coolant side of the cylinder wall, which reduces coolant boiling.
Finally, the engine block employing the secondary cooling chamber of the present invention may be easily adapted to fit heavy duty classes of diesel engines ranging from a cylinder bore diameter and displacement of about 130 mm and about 1.8 liters/cylinder, respectfully (approximately 40 hp/cylinder) to a bore diameter and displacement of about 165 mm and about 4.1 liters/cylinder, respectively (approximately 225 hp/cylinder).